Recently, for treating diseases such as cancer, therapies using a gene transport carrier have been increasingly developed. For example, an anaerobic enteric bacterium, if it is systemically administered, is accumulated in a hypoxic solid tumor. Using this property, a transformed microorganism which can express a gene encoding a protein having an anti-tumor activity or a protein having an activity to convert a precursor of an anti-tumor agent into the anti-tumor agent at a target site of disease (see, for example, Patent Document 1) has been proposed.
Also, an expression cassette, which comprises a promoter, a DNA encoding a signal sequence, a DNA encoding a polypeptide or a cloning site for inserting the DNA (see, for example, Patent Document 2); and a recombinant obligatory anaerobic gram-positive bacterium, which comprises a nucleic acid encoding a fusion protein comprising a signal peptide, a single-chain antibody and one or more heterologous polypeptides and which can express the nucleic acid therein (see, for example, Patent Document 3) have been proposed.
However, signal peptides proposed in the above documents are found in membrane proteins and secretory proteins. In the context, a signal peptide having better secretion efficiency is desirably identified.